If you used objc with OSX 10.10+ before you might have noticed that your code doesn't work on OSX 10.9-. Likewise, your 10.9- code doesn't work on 10.10+. This change solves the compatibility but at the cost of disabling property access via dot notation, which breaks your 10.10+only code. To make it work again, you need to call objc.with_properties(true) after you load objc.